When to start my flowering cycle?

As a general guide flip to flower when you achieved half your desired size. So if you want a 2 ft plant flip when they are 1 ft tall by the end of the flower stretch you should have a 2 ft tall plant. Keep in mind genetics play a role sativa can triple, hybrids can double, some heavy indicas barely stretch at all.

Hi! I suggest that you read about LST, 'cos it can improve your yields easily even in the first grow too! The main idea is to bend the highest tops to same level as the others (Plant hormone called Auxin is stored in the top parts and it tells the plant what is the "main cola" and by lowering that branch you transfer the hormone to create more "mains") and also to get more even light distribution to the plants and to maximize horizontal space in your grow tent. If you try lst'ing then you might want to bend them now and wait maybe week-two and then transfer to flowering and if not I would still wait atleast week-two more to get slightly bigger plant before flipping the switch